If it is an access port then you can set it to Sticky MAC whitelist and limit to 1, just the AP.
However your AP will not be able to have any clients other than those on SSIDs using Meraki DHCP that are NATed by the AP.
If you need trunk mode then there is a new feature where the Meraki AP configures the switchport, so you could leave the initial config on a VLAN with no access and then only a Meraki AP would get connectivity. However you will need a newer AP. Edit, sorry the MR70 is current so this may be an option for you.
I don't think there is a solution for exactly what you have other than locking the AP in a plastic box with the datapoint.
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